Surface conductance and evaporation from 1km to continental scales using remote sensing Ray Leuning, Yonqiang Zhang, Amelie Rajaud, Helen Cleugh, Francis Chiew,
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Surface conductance and evaporation from 1km to continental scales using remote sensing Ray Leuning, Yonqiang Zhang, Amelie Rajaud, Helen Cleugh, Francis Chiew, Lu Zhang & Kevin Tu CSIRO Marine & Atmospheric Research, CSIRO Land & Water 5 February 2008 The challenge Estimate energy & water fluxes at multiple scales CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing MODIS evaporation – a “new” approach • Penman-Monteith equation for surface evaporation: Esurface A ( c p / ) DaGa 1 Ga / Gs • where A available energy Da water vapor deficit Ga aerodynamic conductance Gs surface conductance - we model this s/ CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing Surface evaporation = canopy + soil evaporation Esurface Ecanopy Esoil • PM equation for surface & canopy evaporation • fraction f of equilibrium rate at soil surface: Ga / Gi (1 ) Ga / Gi f 1 Ga / Gs 1 Ga / Gc 1 surface • where canopy As / A = exp( - k A Lai ) A Gi ( c p / ) Da soil MODIS15A2 remote sensing 'climatological conductance' CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing Canopy conductance • Canopy conductance (after Kelliher et al., 1995; Leuning, 1995) g sx Qh Q50 1 Gc ln kQ Qh exp(kQ L) Q50 1 Da / D50 stomatal light humidity deficit CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing Gs sensitivity analysis D A 0.5 200 2.0 f gsx 0.003 0.009 CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing 800 0.8 0.2 Time series for Fluxnet sites: Emeas Eeq Deciduous Evergreen A Eeq 1 CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing Time series for Fluxnet sites: Emeas Eeq Conifer Savanna A Eeq 1 CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing Eeq & ERS versus Emeas for 15 FluxNet sites ERS - PM Equation with Gs & MODIS LAI Eeq - Equilibrium evaporation (c) ERS (mm/d) Eeq (mm/d) (d) Emeas (mm/d) Emeas (mm/d) (e) (f) 2 free parameters: gsx & f CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing Application of ERS to Murray Darling Basin • Long-term water balances of gauged catchments Sw PER0 tav as tav • Thus E PR as tav • Invert evaporation model to solve for gsx & f in model for Gs • Parameters for 3 rainfall zones from 135 catchments, P 450, 450 P 750, P 750 CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing mm/yr Landcover & gauged catchments – Murray Darling Basin CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing Data • Meteorological data • Daily values of solar radiation, Tmin, Tmax and H2O vapor pressure from SILO database, 2000-2005 • MODIS data 2000-2005 • 8-day/1km MOD15A2 LAI from Distributed Active Archive Center of NASA, • Yearly/1km MOD12 land cover • Runoff + rainfall data • Daily runoff at 135 gauged catchments of MDB • Daily precipitation from SILO CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing Time series of E, P & Lai for two catchments near Tumbarumba CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing 5-year average ERS vs EWB for 135 catchments 1000 y = 1.05x 2 R = 0.61 ERS (mm/yr) 800 600 400 200 200 400 600 800 EWB (mm/yr) CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing 1000 P & ERS – Murray Darling Basin CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing Water supply limit Energy limit Remote sensing Zhang CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing Budyko Water balance Runoff: RRs and RBudyko if ERS P, R0 800 800 y = 0.80x R2 = 0.81 RBudyko (mm/yr) RRS (mm/yr) 600 400 200 0 y = 0.87x R2 = 0.59 600 400 200 0 0 200 400 600 800 0 Rmeas (mm/yr) CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing 200 400 Rmeas (mm/yr) 600 800 Runoff maps CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing Conclusions and further work • PM equation, Gs model & MODIS Lai • Builds in energy balance from start • useful for estimating evaporation at catchment scale • Gs model – biophysical with two parameters gsx and f • Overestimation of E due to uncertainties in • MODIS Lai • Single value of f for each rainfall zone – should be variable • No constraint by water balance • Further work • Combine PM combination equation with catchment water balance • Improve soil evaporation component • Use microwave remote sensing for f? CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing CSIRO Marine & Atmospheric Research Ray Leuning Phone: 61 2 6246 5557 Email: [email protected] http://www.dar.csiro.au/lai/ozflux/ Thank you Contact Us Phone: 1300 363 400 or +61 3 9545 2176 Email: [email protected] Web: www.csiro.au